1. Technical Field
The present invention relates to a liquid discharging apparatus, a head unit, and a control method of the liquid discharging apparatus.
2. Related Art
An ink jet printer having piezoelectric elements has been known as an ink jet printer which prints an image or a document by discharging ink. In a head unit, the piezoelectric elements are provided respectively corresponding to a plurality of nozzles. The respective piezoelectric elements are driven in accordance with drive signals, in such a manner that a predetermined amount of ink (liquid) is discharged from the nozzles at a predetermined time. As a result, dots are formed. In an electrical point of view, the piezoelectric element is a capacitive load, such as a capacitor. Thus, when a piezoelectric element corresponding to each nozzle is operated, it is necessary to supply an adequate amount of current to the piezoelectric element.
Therefore, a drive signal amplified by an amplifier circuit is supplied to the head unit, in such a manner that the piezoelectric element is driven. An example of the amplifier circuit includes an amplifier circuit of a type in which a source signal not subjected to amplification is subjected to, for example, class AB current-amplification (in other words, linear amplification) (see JP-A-2009-190287). However, in the case of linear amplification, electric power consumption is large and energy efficiency is not good. Accordingly, in recent years, a configuration in which a source signal is subjected to class D amplification has been proposed (see JP-A-2010-114711).
Meanwhile, in recent years, there has been a high demand for high-speed printing and high-resolution printing of a printing apparatus. To perform high-speed printing, the number of dots formed for each unit time may be increased. To perform high-resolution printing, the number of dots formed for each unit area may be increased in a state where the amount of discharged ink from nozzles is set to be small. In other words, to perform high-speed and high-resolution printing, the number of dots formed for each unit time and unit area may be increased. Thus, a method in which an ink discharge frequency is increased is used.
Meanwhile, to increase an ink discharge frequency, it is necessary to increase the frequency of a drive signal supplied to a piezoelectric element. To perform a stable discharge operation in a state where the frequency of a drive signal is increased and the influence by, for example, residual oscillation, is reduced, it is necessary to increase the switching frequency of class D amplification.
However, when the switching frequency is increased, the loss due to switching is increased. Accordingly, the energy efficiency in class D amplification is reduced to be below the energy efficiency in linear amplification. As a result, it is not possible to ensure high energy efficiency which is an advantage of the class D amplification.
Furthermore, when switching in class D amplification is performed at high frequency, a problem, such as an operational failure due to noise and a heat generation due to switching loss, can occur.
As described above, when the switching frequency of class D amplification is increased to increase the frequency of a drive signal for driving a piezoelectric element, various problems can occur.